This invention relates to improvements in the preparation of dicarboxylic acid anhydrides by the vapor phase oxidation of hydrocarbons and more particularly relates to improvements in the process for the catalytic oxidation of hydrocarbons to dicarboxylic anhydrides in the presence of a vanadium-molybdenum-oxygen catalyst.
It has recently been discovered that high yields of dicarboxylic anhydrides may be obtained by oxidizing hydrocarbons in the vapor phase in contact with a vanadium-molybdenum-oxygen catalyst. Although high yields of dicarboxylic anhydrides have been obtained by such processes, it has been found that the yield of product diminishes with time. It is an object of this invention to provide a method whereby the catalyst may be reactivated and whereby the high yields may be maintained. It has been found as part of the present invention that one reason for the decrease in yield is the deactivation of a portion of the catalyst particles. It is also an object of this invention to selectively activate the deactivated catalyst particles without impairing the activity of the remaining catalyst particles.